I. Field of the Invention
The present invention relates generally to fluid dispensing mechanisms and, more particularly, to an improved modular positive displacement dispenser system of simplified construction in which the dispenser module does not require seals, particularly sliding seals, for its operation, yet applies precisely controlled quantities of the fluid to a receiving surface
Sealants and adhesives, especially of the high viscosity type, are oftentimes difficult to dispense in an accurate and controlled manner. Excessive amounts are wasteful and give a sloppy appearance while insufficient amounts could affect the sealing quality. Moreover, the dispensing should be carried out quickly without compromising on accuracy. II. Description of the Prior Art
There are a number of known designs for dispensing fluids such as adhesives, sealants, and the like, at accurately controlled flow rates, in accurate quantities, and for accurate placement on a receiving surface.
The commonly assigned U.S. Pat. No. 4,347,806 to Argazzi et al issued Sept. 7, 1982 and entitled "Liquid Dispensing Apparatus" discloses a positive displacement type of valve in which a quantity of the fluid is admitted into a chamber whereupon a piston then forces that quantity out through the dispensing outlet or nozzle. In this instance, and in other known instances of the prior art, seals are necessary components of the mechanism and are not totally effective in satisfying their intended purpose.
It is noteworthy that loss of the fluid that does not issue from the outlet nozzle but finds its way instead into other cavities of the dispensing mechanism is a primary concern. In particular, when the fluid is a sealant or adhesive material, it subsequently accumulates, then hardens, and thereby has a detrimental effect on the operation of the dispensing mechanism, even to the point of rendering it inoperative.
A significant improvement in the state of the art occurred with the invention disclosed in the co-pending and commonly assigned application of E. Dickau, entitled "Sealless Dispensing Mechanism", Ser. No. 57,614 filed June 3, 1987 which is hereby incorporated by reference in its entirety. While not a positive displacement pump, that invention relates to a simplified fluid dispenser for dispensing precise quantities of fluid without requiring special seals or springs. It comprises a housing defining a fluid reservoir having an inlet for delivery of pressurized fluid to the reservoir, and including a valve seat defining an outlet for dispensing fluid from the reservoir. A deformable actuator mechanism overlies an open end of the housing opposite the outlet and normally biases a valve engageable with the valve seat to the closed position. When selectively deformed, the actuator is effective to move the valve to the open position to dispense a quantity of the fluid from the reservoir. When released, the actuator returns to its normal condition, returning the valve to the closed position. It is able to dispense fluids having an extremely broad range of viscosities, namely, from one centipoise to a value substantially in excess of one million centipoises.
Furthermore, the dispenser of that invention can be turned on and off instantaneously, that is, starting and stopping a flow of fluid occurs at substantially the same time as operation of the valve actuator. Another significant feature of that invention resides in its construction and manner of operation according to which movement of an actuator used to operate the dispenser causes simultaneous and equal movement of the valve off its seat for dispensing the fluid. This feature allows the dispenser to operate at very high actuation speeds. In actual fact, the dispensing of the fluid is substantially simultaneous with the actuation of the valve.
The contruction disclosed in the aforesaid patent application utilizes no internal seals, especially sliding seals which are particularly susceptible to wear. As a result, the operation of that invention is not hindered by seals which are particularly susceptible to becoming inoperative by being caked or gummed up with dried or partially dried sealant or adhesive material which are commonly dispensed products.